In recent years, the average life expectancy has been increasing, thereby increasing the elderly population because of advances in medicine and science. However, with changes in dietary habits or living environments and the environmental pollution, and new illnesses and infectious diseases due to viruses or fungi have appeared, so that anxiety about people's health has been increasing. Particularly, in the so-called advanced nations, the increase of patients of life-style related diseases such as diabetes mellitus, hypertension or the like has become a problem.
On the other hand, since the number of medical institutions has not so increased as to cope with such increase of patients, and since there are communities where there is no medical institution which patients can attend, there is a concern for how to cope therewith, also from the viewpoint of public policy.
Description will be made below with reference to a specific example. Of the diabetes mellitus patients who are increasing at present, the so-called insulin-dependent type (type 1) diabetes mellitus patients have no secretion of insulin from their pancreas and need to be regularly administered with insulin. Because insulin is administered by subcutaneous injection at present, the physical and mental inconvenience to patients is large.
In order to reduce the inconvenience of such users, a pen-shaped injection syringe has been developed which has a thin needle and causes less pain to a patient. However, because most type 1 diabetes mellitus patients work as able-bodied persons except for requiring regular administration of insulin, they have a mental resistance to injection in public even with a pen-shaped injection syringe, so that it is difficult to administer insulin at the proper times. As a result, with such a method, there is a possibility that the users may not be treated appropriately.
On the other hand, a treatment for a user in which a drug ejection device for allowing the user to intake the drug through inhalation is utilized in combination with information database such as electronic medical records is being embodied. By applying an ink jet system to an ejection mechanism of such a drug ejection device, it is possible accurately to control the liquid droplet diameter and ejection amount of a liquid drug (see International Publications Nos. WO 95/01137 and WO 02/04043).
In an inhaler used in the medical field when atomizing a liquid drug for pulmonary inhalation, not only a system for administrating a drug of a single kind but also a system suitable for mixing/administrating different kinds of drugs has been required. In this case, different kinds of drugs are mixed/administrated by mixing the drugs and encapsulating the mixture in a tank in advance, as long as the drugs thus prepared do not change over time. However, there are also many drugs which need to be administered within a short time after mixing. In such the case, the drugs need to be mixed immediately before the administration.
Further, there are cases where the amounts or kinds of drugs to be administered need to be varied depending on the condition of a user, so that there has been a demand for a method of preparing an ejection liquid in which the composition of the liquid can be easily and surely changed.
Japanese Patent Application Laid-Open No. H11-010859 discloses an example of a liquid ejection device in which liquids are mixed prior to ejection. However, the liquid ejection device adopts a system in which when liquids contained in a plurality of housing parts are mixed, respective liquids are separately supplied through controlling valves and mixed, and thereafter ejected, which requires a complicated structure, and thus has a problem that the system is not suitable for attaining size reduction.
Because it is preferable that the drug ejection device such as described above is so configured as to be portably carried by the user, it is undesirable that the size of the device is increased due to the provision of a mechanism in which liquids are mixed prior to ejection. In other words, the mechanism of mixing liquids prior to the ejection adopted in the conventional liquid ejection device is not suitable for application in the above-mentioned drug ejection device.